This is a collaborative project between Northwestern University (Nelson Spruston and Bill Kath), Stanford University (Stephen Smith), and the University of Bonn (Stefan Remy). The project will lead to an improved understanding of neurons in the hippocampus, which were selected because of their roles in learning and memory as well as a number of cognitive disorders. Studies of these neurons will also offer insight into neurons in other areas of the brain, many of which have shared structural and functional properties. The goals of the project are as follows: We will collect functional data from hippocampal CA1 pyramidal neurons using patch-clamp recording in brain slices combined with two-photon uncaging of glutamate and two-photon calcium imaging. We will also collect structural and molecular data from the same dendritic branches using array tomography, which provides the highest possible resolution using light microscopy. We will examine the distribution of excitatory synaptic weights, as well as the distribution of inhibitory synapses from different interneuron subtypes. All experiments will be performed for dendrites in different dendritic compartments (e.g., basal versus apical dendrites). By performing both functional and structural experiments in the same neurons, we will be able to correlate and integrate the data sets. We will construct compartmental models of CA1 pyramidal neurons, using the data from the experiments to inform improvements on our existing models of these neurons. The models will be used to generate experimentally testable predictions concerning the integration of synaptic inputs. These predictions will extend beyond the range of experiments performed to constrain the model, so they will constitute predictions designed to inform future work on these neurons. Spruston and Kath have a record of using such predictions to design and perform experiments that lead to new discoveries. We will use the models developed in Aim 2 to examine whether stochastic activation of thousands of excitatory and inhibitory synaptic inputs, combined with the excitable properties of the dendrites and synaptic plasticity rules based on the resulting dendritic voltage changes, can lead to non-uniform gradients of excitatory synaptic weights in CA1 pyramidal neurons. Our working hypothesis is that the natural gradients of voltage that exist in CA1 dendrites can contribute to the development of non-uniform synaptic weights. We will compare the results of these simulations to the results from array tomography studies as a means of determining which activity patterns and synaptic plasticity rules best explain the observed distribution of synaptic weights. Collaboration: All team members will exchange data and interact on a regular basis. The Spruston and Remy labs will perform experiments using patch-clamp recording and two-photon uncaging and imaging. Filled cells from these experiments will be sent to Stanford for array tomography in the Smith lab. Spruston, Kath, Smith and Remy will supervise the integration of array tomography data with functional data, working together with the postdoc and student supported by this project. All members of the group will meet regularly to discuss progress and future plans. Intellectual Merit: The project will provide critical data concerning the structure and function of pyramidal neurons in the hippocampus, which will be used to generate computational models of unprecedented detail. The models will be used to advance our understanding of synaptic integration in dendrites and the contribution of excitable dendrites to synaptic plasticity and the distribution of excitatory synaptic weights in the dendritic tree. The underlying philosophy is that the function of neural circuits, as well as diseases that affect them, cannot be understood without an accurate understanding of the structure and function of the component parts in the circuit. Broader Impacts: The broader impacts of this work include international collaboration and international and multi-disciplinary training of students and postdocs. In addition, our experimental data and computational models will be shared with the larger research community. We will also work with Michael Kennedy, Director of Northwestern's Science in Society program, to use our data to generate interactive, web-based educational tools targeting high-school students as well as post-secondary students. Our goal will be to develop visually exciting tools that appeal to a teenage audience. The tools will be promoted through the Science in Society website and through Kennedy's personal interactions with Chicago Public Schools and the Boys & Girls club of Chicago, both of which have large populations of under-served minorities. Stefan Remy will promote these educational tools in Germany. Long term, we believe that these tools could reach national and international audiences.